Traveling wave differential protection(TWDP)is constituted by traveling waves and characterized by two features. First

traveling waves is the composite quantities of voltage and current and inherently contains distributed capacitive current. Second

traveling waves are moving electromagnetic field

whereas transmission delay is the in-evitable attribute of movement. Therefore

TWDP is independent of voltage level

distributed capacitive current and line length. TWDP can be developed by transient quantities or steady quantities. The former solution has a fast operation speed

whereas the latter solution has a strong anti-interference capability. TWDP can be applied to AC transmission lines and DC transmission lines. This paper firstly reviews the research status of TWDP technology at home and abroad

and then systematically summarizes traveling wave characteristics. Next

the challenges faced by TWDP technology are analyzed. Finally

this paper analyzes the applications of TWDP on ultra-high voltage(UHV)AC transmission lines

DC transmission lines

and half-wave length AC transmission lines. The prospects of TWDP technology are also presented.